title: Obstetric and perinatal outcomes in singleton pregnancies resulting from the transfer of blastocyst-stage versus cleavage-stage embryos generated through in vitro fertilization treatment: a systematic review and meta-analysis.
abstract: OBJECTIVE
  To perform a systematic review and meta-analysis of obstetric and perinatal complications in singleton pregnancies after the transfer of blastocyst-stage and cleavage-stage embryos generated through IVF.
  
  
  METHODS
  Systematic review.
  
  
  METHODS
  University hospital.
  
  
  METHODS
  Singleton pregnancies resulting from ET at the blastocyst stage versus those at the cleavage stage.
  
  
  METHODS
  Medline, EMBASE, Cochrane Central Register of Clinical Trials DARE, and CINAHL (1980-2013) were searched. Two independent reviewers extracted data and assessed the methodological quality of the relevant studies using CASP scoring. Risk ratios and risk differences were calculated in Rev Man 5.1.
  
  
  METHODS
  Very preterm birth, preterm birth, small for gestational age, low birth weight, very low birth weight, congenital anomalies, perinatal mortality, preeclampsia, and placenta previa.
  
  
  RESULTS
  In vitro fertilization pregnancies occurring as a result of ET at the blastocyst stage were associated with a higher relative risk (RR; 95% confidence interval [CI]) of preterm (RR 1.27; 95% CI 1.22-1.31) and very preterm delivery (RR 1.22; 95% CI 1.10-1.35) in comparison with those resulting from the transfer of cleavage-stage embryos. The risk of growth restriction was lower in babies conceived through blastocyst transfer (RR 0.82; 95% CI 0.77-0.88).
  
  
  CONCLUSIONS
  Data from observational studies show that ET at the blastocyst stage is associated with a higher risk of very preterm delivery. However, we were not able to adjust for confounders. Perinatal outcome data from existing randomized trials are needed to determine the safety of ET at the blastocyst stage compared with the cleavage stage.
authors.affiliation: Reproductive Medicine, NHS Grampian, Aberdeen, United Kingdom. Electronic address: abha.maheshwari@abdn.ac.uk.
authors.forename: Abha
authors.initials: A
authors.lastname: Maheshwari
authors.forename: Theodoros
authors.initials: T
authors.lastname: Kalampokas
authors.forename: Jill
authors.initials: J
authors.lastname: Davidson
authors.forename: Siladitya
authors.initials: S
authors.lastname: Bhattacharya
mesh_terms: D001755:Blastocyst / Q000473:pathology*; D002970:Cleavage Stage, Ovum / Q000473:pathology*; D015897:Comorbidity; D004624:Embryo Transfer / Q000401:mortality*; D005260:Female; D005307:Fertilization in Vitro / Q000401:mortality*; D006801:Humans; D015994:Incidence; D007230:Infant, Low Birth Weight; D007247:Infertility, Female / Q000401:mortality / Q000628:therapy*; D007744:Obstetric Labor Complications / Q000401:mortality*; D011247:Pregnancy; D011256:Pregnancy Outcome; D015996:Survival Rate; D016896:Treatment Outcome
keywords: ICSI; IVF; blastocyst; cleavage; obstetric outcomes; perinatal outcomes